Exchange Server 5.5

There is a unique problem that I am facing. I am not able to send mails to some email ids outside our exchange server. The error message i am getting is nable to deliver the message due to a communications failure
The MTS-ID of the original message is: c=US;a= ;p=XYZ;l=IXYZMAIL-010913210547Z-161
But the same mail id is reachable from other exchange server totally different from the one I have. It is going perfectly from the private Mail ID’s. From my exchange server other mails to the outside world is going perfectly. Can any one help me out with a solution.

Thanks in Advance